1. Technical Field
The present invention relates to an ion beam irradiation apparatus so constructed as to irradiate a substrate held by a substrate holding surface of a holder with an ion beam that travels in the horizontal direction. Particularly, the invention relates to means for controlling non-uniformity of ion implantation due to a divergent angle of the ion beam applied onto the substrate. This ion beam irradiation apparatus is, for example, an ion implantation apparatus.
2. Related Art
FIG. 4 shows a schematic side view of this type of related-art ion beam irradiation apparatus, showing an example of the constitution in which the substrate held by the holder is irradiated with the ion beam. An ion beam irradiation apparatus having the nearly similar structure to this structure has been disclosed in FIG. 13 in JP-A-2003-110012.
Three axes that are orthogonal to each other at one point are taken as an X-axis, a Y-axis and a Z-axis. Generally, an ion beam 58 traveling in the direction along the Z-axis is scanned in the direction along the X-axis by an electric filed or a magnetic field, and applied onto a substrate 54 held by a substrate holding surface 6 of a holder 4. The holder 4 is, for example, an electrostatic chuck. In this example, both the X-axis and the Z-axis are imaginary axes in the horizontal direction.
Further, as the ion beam 58, in place of the ion beam scanned in the direction along the X-axis, there is also an ion beam which is long in the shape of a strip from its base without scanning in the direction along the X-axis, and travels in the direction along the Z-axis.
In this specification, “direction along an axis” means a direction substantially parallel to its axis. Further, “substantially parallel” includes a parallel state.
This ion beam irradiation apparatus includes a counter-rotatable type of irradiation angle setting motor 14 which controls an irradiation angle θ of the ion beam 58 to the substrate holding surface 6 of the holder 4 supported by a rotation shaft 46 through a coupling member 48, that is, to a surface 56 of the substrate 54 by rotating the holder 4 around the rotation shaft 46 substantially parallel to the X-axis in the direction of an arrow A in FIG. 4; and an elevator unit 50 which causes the holder 4 supported by this motor 14 to ascend and descend in the direction along the Y-axis thereby to scan the substrate 54 for the ion beam 58.
When ion beam 58 irradiation processing for the substrate 54, for example, ion implantation processing is performed, the irradiation angle θ is usually set in a range of 0° to 60°. This irradiation angle θ is an angle made by a perpendicular line 62 to the substrate holding surface 6 and the traveling direction of the ion beam 58. For example, in the ion implantation apparatus, this angle is referred to as an implantation angle.
As described above, in the related-art ion beam irradiation apparatus, in case that the irradiation angle θ is set to an angle that is larger than 0°, the substrate 54 supported by the holder 4, in a tilting state in the irradiation direction of the ion beam 58 (that is, direction along the Z-axis), is scanned in the direction along the Y-axis.
However, in case that the substrate 54, in the tilting state in the irradiation direction Z of the ion beam 58, is scanned in the direction along the Y-axis, there is a problem that the density of the ion beam 58 applied onto the substrate 54 becomes non-uniform in the surface 56 of the substrate 54.
The cause of this problem will be described with reference to FIG. 5. In this figure, for convenience, the irradiation angle setting motor 14, the rotation shaft 46, the coupling member 48 and the elevator unit 50 are omitted.
The ion beam 58 that has passed through a beam slit 52 is applied toward the substrate holding surface 6 of the holder 4 arranged in a vacuum chamber (not shown), that is, the surface 56 of the substrate 54.
The substrate 54, by the reciprocating movement of a center O1 on the surface 56 of the substrate 54 together with the holder 4 between a position α and a position γ, is scanned for the ion beam 58. In a position β, the center O1 on the surface 56 of the substrate 54 coincides with the path of the ion beam 58 traveling in the direction along the Z-axis.
On the other hand, the ion beam 58 is applied in a state where it diverges to some extent in the direction along the Y-axis due to the space-charge effect. Here, the angle at which the ion beam 58 diverges in the direction along the Y-axis is referred to as a divergent angle ξ.
In case that the ion beam 58 is thus applied onto the surface 56 of the substrate 54 in the state where it diverges to some extent in the direction along the Y-axis, according to the distance L from an arbitrary point on the path of the ion beam 58 (for example, an exit point of the beam slit 52) to the surface 56 of the substrate 56, the size of the irradiation region of the ion beam 58 applied onto the surface 56 of the substrate 54 is different. Namely, as the distance becomes longer, the size of the irradiation region of the ion beam 58 applied onto the surface 56 of the substrate 54 becomes larger.
Specifically, the irradiation region of the ion beam 58 applied onto the surface 56 of the substrate 54 when the center O1 on the surface 56 of the substrate 54 is in the position α is taken as G1, the irradiation region of the ion beam 58 applied onto the surface 56 of the substrate 54 when the center O1 on the surface 56 of the substrate 54 is in the position β is taken as G2, and the irradiation region of the ion beam 58 applied onto the surface 56 of the substrate 54 when the center O1 on the surface 56 of the substrate 54 is in the position γ is taken as G3. In this case, among the area of the region G1, the area of the region G2 and the area of the region G3, the relation of G1<G2<G3 holds.
Regarding the density of the ion beam 58 applied onto the surface 56 of the substrate 54, as the area of the irradiation region of the ion beam 58 applied onto the surface 56 of the substrate 54 becomes larger, the density becomes lower; and as the area of the irradiation region of the ion beam 58 applied onto the surface 56 of the substrate 54 becomes smaller, the density becomes higher.
Therefore, in case that the substrate 54 is scanned in the direction along the Y-axis in the titling state in the irradiation direction of the ion beam 58, the distance L changes during irradiation processing of the ion beam 58 onto the surface 56 of the substrate 54. Therefore, a phenomenon is produced in which the density of the ion beam 58 applied onto the substrate 54 becomes non-uniform in the surface 56 of the substrate 54. In result, uniformity of ion implantation in the surface 56 of the substrate 54 worsens.